1. Field of the Invention
The present invention relates to a calibration reflector device for fiber-optic sensors, as well as a sensor arrangement equipped with such a calibration reflector device, particularly for medical use.
2. The Prior Art
Fiber-optic sensors are known in many different embodiments, and are used in medicine, for example, for intravasal measurement of the oxygen saturation in blood. In order to prevent infections, which often have serious consequences, up to and including lethal sepsis, the intravasal part of the sensor must be kept sterile. For other optical measurements to be carried out in situ, including non-medical measurements, the sensor parts to be guided to the measurement site usually must be protected from contamination.
In order to obtain usable measurement results, sensor calibration is generally necessary before the measurement is carried out. For this purpose, calibration reflectors are usually used. These possess reflection properties that are as well-defined as possible. The proportion of the light that is emitted from one or more emitter fibers of the sensor, which portion is reflected by the calibration reflector and detected by the measurement fiber or measurement fibers, serves as the reference value for the actual measurements.
Calibration reflector devices and sensor arrangements of the type stated initially are known from U.S. Pat. No. 4,050,450 and European Patent No. 0 561 126 B1. Usually, conventional calibration reflector devices are clamped to the tip of the sensors to be calibrated. Since the plastics used for the sensors tend to cold-flow under stress, clamping results in permanent deformation, particularly in the case of thin sensors. This deformation interferes both with the introduction of the sensors by way of insertion mechanisms, and with the measurement. Another problem is that no sterilization gas can reach the clamped surfaces. The sensors therefore usually have to be sterilized using gamma rays. However, the gamma radiation used changes the optical properties of the sensors.